This invention relates to filling internal voids in metal components, and more particularly, to a method for simultaneously impressing an electrical current and mechanical compression to metal components containing such internal voids.
Internal voids are common casting defects which normally result from metal shrinkage during solidification or by entrapped gases released upon cooling. Such internal voids (including cracks) can adversely affect the performance of the metal component casting. When the size and/or density of internal voids is less than what is judged allowable, salvage of the metal component is often attempted. The common method for repairing internal voids includes grinding out or otherwise removing portions of the metal component until the internal void is exposed at the ground out surface of the metal component. The resulting grinding cavity and internal void is then metallurgically filled by welding. The aforementioned repair technique is cumbersome, expensive, and time consuming. In some cases the size and/or density of the internal voids is such that the metal component is scrapped and recast.
U.S. Pat. No. 4,068,111 which issued Jan. 10, 1978, illustrates a method for repairing casting defects by removing material from the metal component and providing a smooth cavity. Such method thus necessitates material removal from the metal component casting.
Another commonly used technique for repairing internal voids in castings is hot isostatic pressing (HIP) which generally involves heating a casting in a furnace or other external heating means and then compressing the casting to collapse the internal voids. HIPing thus requires vast heat additions to the casting to make it conducive to compression and thus collapse of the internal voids. The large heating source needed in HIPing is required since heat externally applied to the casting section containing each void tends to flow laterally in the casting and thus dissipate so as to require an extremely large portion of the casting to be heated to the temperature necessary for practical compression thereof. Additionally, where the voids in the casting open to the surface, HIPing can cause oxidation of the internal void surfaces so as to preclude effective filling thereof without first removing such oxide.
Patent 3,606,785 which issued Sept. 21, 1971, illustrates a typical compression of the subject metal components and collapse of internal voids by rolling metal components between rollers. Such technique is most often used immediately following the casting process when the metal component is still in a relatively hot state. Otherwise, the metal component must be reheated with expenditure of large amounts of heat as previously mentioned.